Learn how to create a full screen video background with CSS.
Read on how to do it in this link: https://www.w3schools.com/howto/howto_css_fullscreen_video.asp
Fullscreen Video Background
Learn how to create a full screen video background that covers the entire browser window:
Try it yourself here: https://www.w3schools.com/howto/tryit.asp?filename=tryhow_css_fullscreen_video